Optical element and method for the production thereof

ABSTRACT

A method for producing an optical element, preferably a security feature, wherein a film having a first embossed hologram in an embossing layer is provided, and a second embossed hologram is embossed into the same embossing layer such that the first embossed hologram is partly replaced with the second embossed hologram. The invention further relates to a method for producing an optical element wherein an embossable film provided with an embossed hologram is partly filled with printing lacquer, and a method for producing an optical element wherein hologram embossing is prevented by prior partial printing of the embossing film with curable printing lacquer. The invention relates further to optical features producible by the inventive methods, documents of value having an inventive optical feature and a numbering embosser for use in an inventive production method.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a division of U.S. application Ser. No. 10/479,034,filed May 17, 2004, which is the National Stage of InternationalApplication Serial No. PCT/EP2002/05930, filed May 29, 2002.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to methods for producing an optical element,optical elements producible by said methods, documents of value havingsuch optical elements and a numbering embosser for use in an inventivemethod.

2. Description of the Background Art

Documents, certificates, bank notes, identity cards, plastic cards,etc., can be reproduced true-to-detail and colorfast using modernhigh-resolution color scanners and using color laser printers or thermalsublimation printers. The common availability of color copiers has alsomade it substantially easier to produce high-quality forgeries.

There is therefore a need to make documents, identity cards, bank notes,papers of value, plastic cards, etc., forgery-proof through additionallyapplied security features. Such security features can at least make itmuch more difficult and expensive to produce a high-quality forgery.Known security features are watermarks, silk threads, intertwined linestructures, and the use of special paper. The application of metalizedembossed holograms to bank notes, credit cards and Eurocheque cards hasalso become generally established. Due to the holographic effect, suchembossed holograms can also be used for a special esthetic design ofsuch documents or other objects.

Such embossed holograms are produced e.g. by embossing holographic imagereliefs into an embossable film in bulk. An adhesive layer is applied tothe embossed film. Further design is therefore no longer possible. Withthe adhesive layer the embossed film is applied e.g. as a securityfeature.

However, such simple embossed holograms likewise offer only limitedprotection from forgery. The increasing spread of correspondingtechnology already makes it possible to imitate such embossed holograms.

It would therefore be desirable if methods were available for producingoptical elements whose forgery is further impeded and that permit simpleindividualization. It is the problem of the present invention to specifycorresponding methods for producing optical elements, optical elementsthat are difficult to forge, documents of value having such opticalelements and an embossing tool for use in a production method.

SUMMARY OF THE INVENTION

In a first inventive method, an embossable film or substrate surfacehaving a first embossed hologram is first provided. Said embossedhologram can have been embossed into an embossable film as a holographicimage relief in the known way. Thus, the first embossed hologram in theembossing layer of said film is mass-producible. In the inventive methoda second embossed hologram is embossed into the same embossing layerwhere the first embossed hologram is already formed. According to theinvention, the second embossed hologram partly replaces the firstembossed hologram.

In the inventive method two embossed holograms are thus embossed intoone another. The second embossed hologram can be selected so that itholographically reconstructs a different image from the first embossedhologram when illuminated. When the second embossed hologram is viewed adifferent optical effect arises than when the surfaces bearing the firstembossed hologram are viewed. The optical structures, e.g. diffractiongratings of embossed holograms, have typical orders of magnitude andspacings of a few hundred nanometers and are thus not recognizable withthe naked eye. Only when illuminated with corresponding reconstructionlight and viewed at the holographic reconstruction angle does theholographically stored information become visible. Unlike e.g. twoadhesive holograms that have been glued one above the other, the twoembossed hologram structures present in one embossing layer can thusnormally not be recognized by simple viewing with the naked eye. Onlyillumination with reconstruction light and viewing at the correspondingreconstruction angle make the double structure recognizable.

The inventive method can thus be used to produce an optical element thatfirstly causes a special optical, and possibly especially esthetic,effect. Additionally, the structure having a plurality of differentembossed holograms in one embossing layer is more difficult to imitate.This results in a higher recognition value, which can also be checkedeasily without special equipment.

Embossing the second embossed hologram structure into the same embossinglayer as the first embossed hologram structure permits simpleproduction. It is not necessary to glue different layers onto each otheror interconnect them.

Further embossing steps can of course be provided for further embossedholograms that partly replace the first and/or previously formedembossed holograms.

The second embossed hologram structure can have the same external formfor all optical elements. However, a significant increase inforgery-proofness and/or range of application is given if the secondembossed hologram is different for each optical element. In this way theoptical element can be individualized as a security feature, e.g. in theform of a consecutive registration number.

In advantageous embodiments, the first and second embossed hologramshave different reconstruction angles and/or different reconstructionwavelengths.

Additional information can be represented if the external form of thesecond embossed hologram can likewise convey information. The firstembossed hologram is then replaced with the second embossed hologram inthe form of the external form of the latter. Upon viewing of the opticalelement, the information stored in the first embossed hologram or theinformation stored in the second embossed hologram thus becomes visibledepending on the viewing angle or viewing light. It additionally becomesrecognizable what external form the second embossed hologram has. Forexample, the second embossed hologram can have the external form of anumber. This number can e.g. correspond to the serial number of adocument of value.

While the first embossed hologram can be formed in the embossing layerof the film in bulk, the second embossed hologram can be embossedindividually for each single optical feature in the form of a differentnumber. This permits the optical features to be individualized verywell.

The inventive method can be carried out especially simply using anumbering embosser which advantageously comprises metallic positive ornegative numbers produced by etching or engraving technology and eachhaving a holographic relief applied thereto. If the numbers of thenumbering embosser already bear the holographic relief for the secondembossed hologram on the embossing surface, the numbering process forproducing the second embossed hologram can be performed as in acustomary numbering embossing process. While a first embossed hologramis being brought into the embossing position for the second embossedhologram, the numbering tool switches to the desired number. The secondembossed hologram is embossed into the embossing layer of the firstembossed hologram layer in the external form of the desired number.Subsequently, an adhesive layer is e.g. applied to the back and theoptical feature glued to the object to be protected, e.g. a document ofvalue. A further first embossed hologram is brought into the positionfor embossing the second embossed hologram while the numbering embosseradvances one number. The process is now repeated accordingly.

The holographic relief on the embossing surface of the numbering toolcan be e.g. a corresponding nickel master bearing the embossed structureof the second embossed hologram in metallic form.

In another advantageous embodiment, a nickel band having a holographicrelief is placed over the number wheel of an embossed numbering unit.The embossing surfaces of the numbering unit then need not be providedwith the holographic relief themselves. In the embossing process for thesecond embossed hologram the embossing surface of the particular numberof the numbering embosser presses the nickel band having the holographicrelief into the embossing layer of the first embossed hologram. In theexternal form of the particular number of the numbering embosser theholographic relief structure of the nickel band is thus embossed intothe embossing layer of the first embossed hologram.

An inventive optical element that can be used in particularadvantageously as a security feature for documents of value comprises afirst embossed hologram in an embossing layer and a second embossedhologram in the same embossing layer. The second embossed hologram isdisposed within the external outlines of the first embossed hologram.

In such an inventive method, an embossable film or substrate surface isprinted partly with a curable printing lacquer. Subsequently saidlacquer is cured. In a further method step an embossed hologram isembossed onto the thus partly printed substrate, the cured lacquerpreventing embossing in the printed partial areas. Such an inventivemethod likewise permits the representation of information by theexternal form of the surface printed with the cured lacquer. The imagethat is reconstructed holographically when the embossed hologram isilluminated leaves out the printed partial areas. In this way theinformation represented e.g. in the external form of the printed areasis visible.

In a further inventive method, an embossable film or substrate surfacehaving an embossed hologram is first provided. To said embossed holograma printing lacquer is applied in partial areas to fill the embossedrelief structure of the hologram. Optionally, the lacquer issubsequently cured. This inventive method thus also produces an opticalelement whose embossed hologram is left out in partial areas. Again, thepartial areas can have an external form of information, e.g. a number.Upon illumination of the embossed hologram, the filled partial areas donot reconstruct the image stored in the hologram, so that theinformation stored by the external form becomes recognizable.

In the latter inventive method, it is thus possible in a simple way torepresent additional information going beyond what is reconstructedholographically by the embossed hologram. Application of the printinglacquer is possible in a simple way and optionally individually for eachsingle optical element. This guarantees high forgery-proofness.

In these inventive methods using printing lacquer, the external form ofthe printed partial areas can again correspond to an individual number,thereby permitting e.g. a consecutive registration of optical elementsor the security features or documents of value provided therewith.

The printing lacquer can be applied to the embossing film in differentways. Application is especially simple and reliable using a jet printer,similar to an ink jet printer, which applies the lacquer in the desiredexternal form. Application with a laser printer also permits simple andreliable design.

It is especially advantageous if the printing lacquer is transparent orcolored-transparent. Such an embodiment increases the forgery-proofnessof the finished optical element since the surface in the partial areasdoes not differ from the surrounding embossed hologram areas by acompletely different color or transmission.

The optical element produced with an inventive method can be used andfastened in different ways, e.g. as a security element. It is especiallysimple and thus advantageous if an adhesive layer for fastening theoptical element to the object to be protected is applied to theunembossed side only after all embossing processes have been performed.An adhesive layer attached only after all embossing processes have beenperformed does not hinder the embossing processes.

It is especially advantageous to use an adhesive coating in the form ofa hot-melt adhesive coating which can be treated thermally.

In all inventive methods, a metalization or coating with a highlyrefractive material is advantageously performed at the end of theproduction process but at least only after all embossing processes, forprotecting the structure or making the holographic effect wellrepresentable.

For the inventive method one can use embossable substrate surfaces, inparticular and especially advantageously hot stamping foils, stickerembossing films, paper coated with thermal lacquer or substrate surfacescoated with UV lacquer.

An inventive optical element of another embodiment, which can likewisebe used in particular advantageously as a security feature for documentsof value, comprises an embossed hologram in an embossing layer, wherebyat least one partial area of the relief embossed into the embossinglayer is filled so that no holographic reconstruction can take place inthe partial area.

It is especially advantageous to use the inventive methods and opticalelements in documents of value, e.g. as a security feature.

BRIEF DESCRIPTION OF THE DRAWINGS

Hereinafter the invention will be explained in detail with reference topreferred embodiments and designs. The figures show examples ofinventive embodiments in a schematic representation, whereby

FIG. 1 shows an inventive document of value having an inventive opticalfeature,

FIG. 2 shows an inventive optical element,

FIG. 3 shows another embodiment of an inventive optical element,

FIG. 4 shows an embossing die of an inventive numbering embosser,

FIG. 5 shows the plan view of an inventive optical element according toa further embodiment, and

FIG. 6 shows a cross section along line A-A in FIG. 5.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a schematic representation of e.g. bank note 1. Said banknote has applied thereto in known fashion information, e.g. the valueand image information, which is of little interest here and accordinglynot included in the figure. Bank note 1 optionally contains varioussecurity features, such as watermarks or guilloches, which are likewiseomitted here.

Number 3 designates an inventive security feature on inventive bank note1. Inventive security feature 3 includes, among other things, number 5,in the shown example the number “123.”

FIG. 2 shows the inventive security feature of this embodiment in anenlarged representation. It comprises first embossed hologram 30, whichis shown only schematically in the form of lines. Said first embossedhologram can be a diffraction grating. The spacing of the individualgrating stripes is typically a few hundred nanometers to permitinterference effects of visible light to be produced in known fashion.The invention is of course not limited to such stripe-shaped holograms,but can have any desired forms of embossed hologram representingdifferent information holographically, e.g. the image of athree-dimensional object.

In the same layer of first embossed hologram 30 there is a secondembossed hologram, whose embossed structure 50 is again shown only in anextremely schematic representation in the form of lines. A possibleembodiment again comprises a diffraction grating similar to diffractiongrating 30. However, the spacing of the individual grating stripes isdifferent, so that a different wavelength interferes in this diffractiongrating compared to the first embossed hologram. Second embossedhologram 50 reconstructs in a different direction, which isschematically indicated by the different direction of hatching in FIG.2. It is of course also true of second embossed hologram 50 that anyother holographic information can be stored, e.g. the three-dimensionalholographic image of an object.

The external form of second embossed hologram 50 shows the number “123”in the shown example.

FIG. 3 shows an embodiment in which second embossed hologram 51, againindicated extremely schematically only as hatching, has gaps in the formof digits. In gaps 31 first embossed hologram 30 becomes visible. Thus,the digits of the number “123” shown by way of example are bordered bysecond embossed hologram 51.

FIG. 4 shows the embossing die of an inventive embodiment of a numberingembosser. Embossing die 7 is shown for structure 9, the digit “1” here.On embossing side 13 the digit “1” is formed in raised fashion in alaterally reversed representation. On the embossing surface of theraised digit, embossing structure 11 for an embossed hologram is appliedas a nickel master. Here, too, the representation is of course indicatedextremely schematically only as hatching.

Inventive optical elements can be produced by an inventive method asfollows.

First, first embossed hologram 30 is formed in conventional fashion inan embossable film, which either is formed completely as an embossinglayer or comprises an embossing layer. For example, the embossing layercan be a thermal lacquer layer in which a hologram is hot stamped inknown fashion. For this purpose the desired embossed hologram structureis embossed using a hot stamping die. This process can be effected inmass production. For example, the first embossed hologram structure canbe embossed on a larger film unit and cut later.

The thus produced film having first embossed hologram 30 in theembossing layer is supplied to a numbering tool suitable for embossingconsecutive numbers. This embossing tool is used to emboss a number intothe same embossing layer where first embossed hologram 30 is located andthus replaces the embossed structure of the first embossed hologram inthe external form of the embossing surface of the embossing die of thenumbering tool. Second embossed hologram 50, 51 is thus embossed intofirst embossed hologram structure 30 in the external form of the numbersof the numbering tool.

Various forms for the numbers are conceivable. For example, the numbersof the second embossed hologram structure can represent a numberpositively, as shown in FIG. 2, or appear as a border in negative form,as e.g. in FIG. 3.

FIG. 4 shows e.g. embossing die 7 for a positive digit “1.” The secondembossed hologram structure is located e.g. as a nickel master onembossing surface 11 of an embossing die of the numbering tool. In analternative embodiment, a nickel band bearing the structure forembossing the second embossed hologram is placed around the number wheelof the numbering embosser. During embossing, the structure of the nickelband is molded into the embossing layer of the first embossed hologramusing the numbering tool, without the embossing surfaces of thenumbering wheel having to be structured themselves.

FIG. 5 shows further inventive security feature 3 which can be providedon bank note 1. As shown in FIG. 1, the security feature according tothis embodiment again comprises number 5, in the shown example thenumber “123.”

The inventive security feature of this embodiment comprises embossedhologram 63, which is again shown only schematically in the form oflines. Said embossed hologram can also be a diffraction grating whosegrating spacing is typically a few hundred nanometers to permitinterference effects of visible light to be produced in known fashion.The embossed hologram is of course not limited to such stripe-shapedholograms here either but can have any desired forms of embossedhologram that represent different information holographically, e.g. theimage of a three-dimensional object.

Within the outlines of embossed hologram 63 there are areas 61 that donot bear any embossed structure like surrounding embossed hologram 63.This can be obtained by different proceduress, which are describedbelow.

In areas 61 there is no holographic reconstruction upon illumination, sothat the holographic effect is left out in said areas. Total securityfeature 3 thus shows a holographic effect, e.g. the representation of athree-dimensional object. Only partial areas 61 in the external form ofthe number “123” fail to reconstruct an image holographically, so thatthey are recognizable and the information of their external form isvisible.

Such an inventive optical feature can be produced as follows. Embossedhologram 63 is formed in conventional fashion in an embossable film,which either is formed completely as an embossing film or comprises anembossing layer. The embossing layer can e.g. be a thermal lacquer layerin which a hologram is hot stamped in known fashion. For this purposethe desired embossed hologram structure is embossed using a hot stampingdie in this embodiment as well. This process can be effected in massproduction, e.g. embossed on a larger film unit and cut later.

A laser printer or jet printer, similar to an ink jet printer, is usedto apply printing lacquer 61 to embossed hologram structure 63 in thedesired external form, here the number “123,” thereby filling the reliefof the embossed hologram structure. This is visible in cross section inFIG. 6. In the areas filled with lacquer 61, embossed hologram layer 63no longer reconstructs holographically when illuminated withreconstruction light.

In another inventive method, printing lacquer 61 is applied to anembossable film in a desired external form, e.g. in the shape of thenumber “123,” with a laser printer or jet printer, similar to an ink jetprinter, before the embossed hologram is embossed. After a curing stepfor the printing lacquer, the film thus provided partly with printinglacquer is embossed in the way known for embossed holograms, therebyproducing embossed hologram 63. In the areas printed with lacquer 61,embossing is prevented during the embossing step so that here, too,there can be no holographic reconstruction in the completed opticalelement.

In all described embodiments, a hot-melt adhesive layer for fasteningthe optical element to document of value 1 is applied to the back ofoptical element 3 only after all necessary embossing processes have beenperformed. Since said adhesive layer is applied only after all embossingprocesses, it cannot disturb the prior method steps.

In all inventive embodiments, the embossable substrate surface used canbe a hot stamping foil, sticker embossing film, paper coated withthermal lacquer or substrate surface coated with UV lacquer. Theinvention is not limited to single number 5. The method and opticalfeatures are especially advantageous when the external form ofholographic area 50, 31 reconstructing differently or area 61 notreconstructing holographically at all is a consecutive number that isallotted individually to each optical element. This makes it possible toindividualize the particular optical element, e.g. in the manner of aregistration number for a document of value.

1. A method for producing an optical element, having the followingsteps: a²) printing partial areas of an embossable film or substratesurface with a curable printing lacquer, curing the printing lacquer,and b²) embossing an embossed hologram on the printed substrate, thecured printing lacquer preventing embossing in the printed partialareas.
 2. A method for producing an optical element, having thefollowing steps: a³) providing an embossable film or substrate surfacehaving an embossed hologram in an embossing layer, b³) applying aprinting lacquer in partial areas of the embossed hologram structuresuch that the relief structure of the embossed hologram structure isfilled with printing lacquer in the partial areas, and c³) after saidapplying step, metalizing or coating with a highly refractive materialon the embossed side of the optical element.
 3. A method according toclaim 2, wherein in step b²) the printing lacquer is applied in anexternal form representing information.
 4. A method according to claim2, wherein step b²) is performed for individualizing the opticalelement.
 5. A method according to claim 4, wherein in step b²) theprinting lacquer is applied in an external form having an individualexternal form for single optical elements.
 6. A method according toclaim 5, wherein the external form comprises the form of an individualnumber.
 7. A method according to claim 2, wherein the printing lacqueris applied with the desired external form with a jet printer or laserprinter.
 8. A method according to claim 2, wherein the printing lacqueris transparent or colored-transparent.
 9. A method according to claim 2,wherein after step b³), an adhesive coating is applied to the unembossedside of the film.
 10. A method according to claim 2, wherein in step a³)embossable substrate surfaces, selected from the group consisting of hotstamping foils, sticker embossing films, paper coated with thermallacquer and substrate surfaces coated with UV lacquer, are used.
 11. Adocument of value having an optical feature produced by a methodaccording to claim
 2. 12. A method according to claim 1, wherein in stepb¹) the printing lacquer is applied in an external form representinginformation.
 13. A method according to claim 1, wherein step b²) isperformed for individualizing the optical element.
 14. A methodaccording to claim 13, wherein in step b²) the printing lacquer isapplied in an external form having an individual external form forsingle optical elements.
 15. A method according to claim 14, wherein theexternal form comprises the form of an individual number.
 16. A methodaccording to claim 1, wherein the printing lacquer is applied with thedesired external form with a jet printer or laser printer.
 17. A methodaccording to claim 1, wherein the printing lacquer is transparent orcolored-transparent.
 18. A method according to claim 1, wherein afterstep b²), an adhesive coating is applied to the unembossed side of thefilm.
 19. A method according to claim 1, wherein in step a²) embossablesubstrate surfaces, selected from the group consisting of hot stampingfoils, sticker embossing films, paper coated with thermal lacquer andsubstrate surfaces coated with UV lacquer, are used.
 20. A document ofvalue having an optical feature produced by a method according toclaim
 1. 21. An optical element having an embossed hologram in anembossing layer and at least one partial area in the embossing layer inwhich the relief of the embossed hologram structure is left out, whereinin the non-embossed partial area there is disposed a cured lacquer onthe embossing layer.
 22. An optical element according to claim 21,wherein the at least one partial area comprises an individual externalform, in a form of a number either in positive or negativerepresentation.
 23. An optical element according to claim 21, whereinthe film is provided with an adhesive layer on the unembossed side. 24.A document of value having an optical element according to claim 21.